Silica

ABSTRACT

Silanized, structurally modified, pyrogenically produced silicas, characterised by groups fixed to the surface, wherein the groups are dimethylsilyl and/or monomethylsilyl, are produced in that pyrogenically produced silica is treated by a known method with dimethyldichlorosilane and/or monomethyltrichlorosilane, the groups dimethylsilyl and/or monomethylsilyl being fixed on the surface of the pyrogenic silica, and is then structurally modified and optionally post-ground. They are used to improve scratch resistance in lacquers.

INTRODUCTION AND BACKGROUND

The invention relates to a silanised, structurally modified,pyrogenically produced silica, a process for the production thereof andits use.

It is known to use nanoscale particles in transparent coatingcompositions.

Thus, according to U.S. Pat. No. 6,020,419, pyrogenically producedsilicon dioxides, deagglomerated in situ, which have been madehydrophobic with dimethyldichlorosilane (Aerosil® R 972), are used inpolyurethane lacquers to improve the scratch resistance of the coatings.

The known silica has the disadvantage that it cannot be produced inpowder form without a lacquer binder.

The object therefore existed of developing a silica that does not havethese disadvantages.

SUMMARY OF THE INVENTION

The present invention provides silanised, structurally modified,pyrogenically produced silicas, which are characterised by groups fixedon the surface, the groups being dimethylsilyl and/or monomethylsilyl,preferably dimethylsilyl.

In a preferred embodiment of the invention the silicas can have thefollowing physico-chemical characteristics:

BET surface area m²/g: 25-400 Average size of the primary particles nm:5-50 pH value: 3-10 Carbon content %: 0.1-10   DBP value %: <200

The silica according to the invention can have a tamped density of 100to 280, preferably 100 to 240 g/l.

A tamped density of more than 280 g/l leads to poorer results in thetechnical lacquer tests.

Pyrogenic silicas are known from Winnacker-Küchler ChemischeTechnologie, volume 3 (1983) 4th edition, page 77 and UllmannsEnzyklopädie der technischen Chemie, 4th edition (1982), volume 21, page462.

In particular, pyrogenic silicas are produced by flame hydrolysis ofvaporisable silicon compounds, such as e.g. SiCl₄, or organic siliconcompounds, such as trichloromethylsilane.

The invention also provides a process for the production of thesilanised, structurally modified, pyrogenically produced silicasaccording to the invention, which is characterised in that pyrogenicallyproduced silica is treated with dimethyldichlorosilane and/ormonomethyltrichlorosilane by a known method, the dimethylsilyl and/ormonomethylsilyl groups being fixed on the surface of the pyrogenicsilica, and is then structurally modified and optionally post-ground.

In one embodiment of the invention a tempering can take place after thestructural modification and/or post-grinding.

The silicas according to the invention can be produced e.g. as follows:

The silicas, which can be produced as described in DE 1 163 784, arethen structurally modified by mechanical action and possibly post-groundin a mill. A tempering can possibly take place after the structuralmodification and/or post-grinding.

The structural modification can take place e.g. with a ball mill or acontinuously operating ball mill. The post-grinding can take place e.g.using an air-jet mill or pin mill. The tempering can take placebatchwise, e.g. in a drying cupboard, or continuously, e.g. in afluidised bed. The tempering can take place under protective gas, e.g.nitrogen.

The silicas according to the invention can be incorporated intolacquers, as a result of which these lacquers have increased scratchresistance.

DETAILED DESCRIPTION OF INVENTION Examples

Production and Physico-chemical Properties of the Silicas

Production of the Comparative Silicas:

The production of the comparative silicas 1, 2 and 3 takes place asdescribed in DE 1 163 784.

Production of the silicas according to the invention:

The silicas, which are produced as described in DE 1 163 784, are thenstructurally modified by mechanical action and possibly post-ground in amill. A tempering can possibly take place after the structuralmodification and/or post-grinding.

The structural modification can take place e.g. with a ball mill or acontinuously operating ball mill. The post-grinding can take place e.g.using an air-jet mill or pin mill. The tempering can take placebatchwise, e.g. in a drying cupboard, or continuously, e.g. in afluidised bed. The tempering can take place under protective gas, e.g.nitrogen.

TABLE 1 Overview of the production of the comparative silicas and thesilicas according to the invention (Examples) Post-grindingSurface-fixed Structural after structural Tempering after Designationgroup modification modification post-grinding Comparative silica 1Dimethylsilyl No — — Comparative silica 2 Dimethylsilyl No — —Comparative silica 3 Dimethylsilyl No — — Silica 1 Dimethylsilyl Yes NoNo Silica 2 Dimethylsilyl Yes No No Silica 3 Dimethylsilyl Yes No NoSilica 4 Dimethylsilyl Yes No No Silica 5 Dimethylsilyl Yes Yes NoSilica 6 Dimethylsilyl Yes No No Silica 7 Dimethylsilyl Yes Yes NoSilica 8 Dimethylsilyl Yes Yes Yes Silica 9 Dimethylsilyl Yes Yes YesSilica 10 Dimethylsilyl Yes Yes No Silica 11 Dimethylsilyl Yes Yes No

TABLE 2 Physico-chemical data of the silicas according to the invention(Examples) and the comparative silicas Temped Loss on Loss on C DHP HRTspecific density dying ignition pH content adsorption surface areaDesignation [g/l] [%] [%] value [%] [%] [m³/g] Comparative 64 0.1 0.54.0 0.8 243 113 silica 1 Comparative 67 0.5 0.6 4.8 1.0 256 165 silica 2Comparative 72 0.7 1.0 4.0 1.6 255 256 silica 3 Silica 1 236 0.1 0.6 4.00.8 127 115 Silica 2 204 0.1 0.6 3.9 0.8 137 116 Silica 3 223 0.3 0.74.2 1.0 160 169 Silica 4 186 0.3 0.7 4.2 1.1 152 171 Silica 5 109 0.20.7 4.4 1.1 159 167 Silica 6 193 1.2 0.7 5.2 1.7 157 258 Silica 7 1250.2 0.7 4.1 0.8 130 110 Silica 8 108 0.7 1.3 5.0 1.7 156 257 Silica 9123 0.3 0.5 4.3 1.1 157 165 Silica 10 102 0.7 1.2 6.2 1.7 164 256 Silica11 160 0.2 0.7 4.0 0.8 132 115

Example 1

For the investigation of the improvement in scratch resistance, aconventional 2-component polyurethane lacquer was used. The formulationof the lacquer and its production, including application, are summarisedbelow:

Formulation

Parts by wt. Millbase Acrylic copolymer, mod. with synthetic fatty 43.4acids, 60% solution Butyl acetate 98% 17.8 Xylene 3.9 AEROSIL 5.0 Σ 70.7Lacquer make-up Xylene 11.3 Ethoxypropyl acetate 3.4 Butyl glycolacetate 1.6 Aliphatic polyisocyanate, approx. 75% in 1- 18.6methoxypropyl-2-acetate/xylene 1:1 Σ 105.0

-   Binder concentration: 40%-   AEROSIL calculated on the basis of millbase (solids): 19.2%-   AEROSIL calculated on the basis of lacquer (total): 5.0%-   AEROSIL calculated on the basis of lacquer (solids): 12.5%    Production and Application of the Lacquers

The binder is mixed with the solvents. Then, for the purpose ofpredispersion, the AEROSIL is incorporated into this mixture with thehigh-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm.The mixture is dispersed in a laboratory pearl mill for 30 min at 2500rpm and 60% pump capacity using glass beads (Øapprox. 1 mm). Themillbase is tested with a grindometer, 25 μm, in accordance with DIN ISO1524. It must be smaller than 10 μm.

The conversion of the millbase to lacquer takes place in accordance withthe formulation, the components being mixed with a vane agitator at 2000rpm. The hardener is incorporated in the same way.

After adjusting the lacquers to spray viscosity in accordance with DIN53411, the lacquers are applied to black lacquered metal sheets, e.g. DT36 (from Q-Panel), by spray application (coat thickness about 40-50 μm).After spraying, the metal sheets are dried for 24 h at room temperatureand then for 2 h in a drying oven at 70° C.

Scratch Tests:

The metal sheets are abraded with a quartz/water slurry (100 g water +1g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washingresistance tester (Erichsen, brush with hog's bristles). The glossbefore and 10 min after the abrading is determined with a reflectometer(20° irradiation angle).

TABLE 3 Summary of the properties of the liquid lacquers relevant interms of lacquer technology, and of the applied and dried films.Comparative Silica Silica Comparative Silica Silica silica 1 1 2Reference silica 2 3 4 Reference Grindometer value [μm] <10 <10 <10 /<10 <10 <10 / Viscosity (millbase) [mPas]  6 rpm 4710 421 772 571 4990802 772 55 60 rpm 1120 210 264 225 1200 279 264 52 Viscosity (lacquer +hardener) [mPas]  6 rpm 882 105 210 135 857 235 105 70 60 rpm 239 75 9279 242 100 26 37 Flow Orange-peel OK OK OK Orange-peel OK OK OK Scratchresistance 20° reflectometer value 39.0 83.4 83.5 88.8 67.2 84.2 82.689.3 before scratching Haze before scratching 430 30 40 3 235 18 10 2 40strokes with Sikron F 500 / 83.7 82.3 56.0 / 74.7 80.4 47.2 residualgloss [%]

The silicas 1+2 and 3+4 according to the invention can be used in highconcentrations without impairing the appearance of the lacquer surfaceowing to their substantially lower rheological efficiency compared withcomparative silicas 1 and 2. In addition, the silicas according to theinvention display a substantial improvement in the scratch resistance ofthe lacquer surface.

Example 2

In this example the influence of the structural modification wasinvestigated on the basis of a high solids 2-component PU clear lacquer.The formulation of the lacquer and its production, including applicationand testing, are summarised below:

Formulation

Parts by wt. Millbase Acrylic copolymer, mod. with synthetic 61.0 fattyacids, 70% in n-butyl acetate Butyl acetate 98% 7.3 Methoxypropylacetate 1.7 Solvesso 100 2.0 Xylene 2.0 Baysilon OL 17, 10% in xylene0.7 (silicone oil) AEROSIL 5.0 Σ 79.7 Lacquer make-up (hardener)Aliphatic polyisocyanate, 90% in n- 22.3 butyl acetate Butyl acetate 98%2.0 Solvesso 100 1.0 Σ 105.0

-   Binder concentration: 62.8%-   Aerosil calculated on the basis of millbase (solids):11.7%-   Aerosil calculated on the basis of lacquer (total): 5.0%-   Aerosil calculated on the basis of lacquer (solids): 8.0%    Production and Application of the Lacquers

The binder is mixed with the solvents. Then, for the purpose ofpredispersion, the AEROSIL is incorporated into this mixture with thehigh-speed mixer (disk Ø45 mm) and predispersed for 5 min at 2000 rpm.The mixture is dispersed in a laboratory pearl mill for 30 min at 2500rpm and 60% pump capacity using glass beads (Ø approx. 1 mm). Themillbase is tested with a grindometer, 25 μm, in accordance with DIN ISO1524. It must be smaller than 10 μm.

The conversion of the millbase to lacquer takes place in accordance withthe formulation, the components being mixed with a vane agitator at 2000rpm. The hardener is incorporated in the same way.

After adjusting the lacquers to spray viscosity in accordance with DIN53411, the lacquers are applied to black lacquered metal sheets, e.g. DT36 (from Q-Panel), by spray application (coat thickness about 40-50 μm).After spraying, the metal sheets are dried for 24 h at room temperatureand then for 2 h in a drying oven at 70° C.

Scratch Tests:

The metal sheets are abraded with a quartz/water slurry (100 g water +1g Marlon A 350, 0.25%+5 g Sikron F500) using an abrasion and washingresistance tester (Erichsen, brush with hog's bristles). The glossbefore and 10 min after the abrading is determined with a reflectometer(20 ° irradiation angle).

TABLE 4 Summary of the properties of the liquid lacquers relevant interms of lacquer technology, and of the applied and dried films.Comparative silica 2 Silica 3 Silica 4 Reference Grindometer value [μm]<10 <10 <10 / Viscosity (millbase) [mPas]  6 rpm 6200 1500 541 140 60rpm 2100 900 559 195 Viscosity (lacquer + hardener) [mPas]  6 rpm 38211041 497 167 60 rpm 1320 666 446 195 Flow marked OK OK OK orange-peel20° reflectometer value 81.0 83.5 82.8 88.0 before scratching Haze 25 56 2 40 strokes with Sikron 94.3 93.4 82.0 F 500 residual gloss [%]

The silicas 3+4 according to the invention can be used in highconcentrations without impairing the appearance of the lacquer surfaceowing to their substantially lower rheological efficiency compared withcomparative silica 2. In addition, the silicas according to theinvention display a substantial improvement in the scratch resistance ofthe lacquer surface.

Example 3

Direct comparison of the silicas according to the invention with ascratch-resistant lacquer according to DE 198 11 790 A1, in whichAEROSIL R 972 is used to improve the scratch resistance.

Silicas 2) Prior according to art 1) the invention Millbase Desmophen A2009/1 190.2 Methoxypropyl acetate: 36.8 Solvesso 100 1:1 AEROSIL 23.0 Σ250.0 Lacquer make-up Desmophen A YEP4-55A, 96.0 — contains AEROSIL R972 Millbase — 48.9 Desmophen 2009/1 — 24.9 OL 17, 10% in MPA — —Modaflow 1% in MPA — — MPA: Solvesso 100 1:1 11.6 33.8 Butyl glycolacetate 10.5 10.5 Byketol OK 7.5 7.5 Byk 141 0.8 0.8 Hardener additionDesmodur N 3390 23.6 23.6 Σ 150.0 150.0Production and Application of the Lacquers

-   1) Comparative silica 1 is incorporated into the binder in    accordance with DE 198 11 790 Al using a jet disperser.-   2) The binder is mixed with the solvents. Then, for the purpose of    predispersion, the AEROSIL is incorporated into this mixture with    the high-speed mixer (disk Ø45 mm) and predispersed for 5 min at    2000 rpm. The mixture is dispersed in a laboratory pearl mill for 30    min at 2500 rpm and 60% pump capacity using glass beads (Øapprox. 1    mm). The millbase is tested with a grindometer, 25 μm, according to    DIN ISO 1524. It must be smaller than 10 μm.

The conversion to lacquer of the millbases corresponding to 1) or 2)takes place in accordance with the formulation, the components beingmixed at 2000 rpm with a vane agitator. The hardener is incorporated inthe same way.

After adjusting the lacquers to spray viscosity in accordance with DIN53411, the lacquers are applied to black lacquered metal sheets, e.g. DT36 (from Q-Panel), by spray application (coat thickness about 40-50 μm).After spraying, the metal sheets are dried for 24 h at room temperatureand then for 2 h in a drying oven at 70° C.

Scratch Tests:

The metal sheets are abraded with a quartz/water slurry (100 g water+1 gMarlon A 350, 0.25%+5 g Sikron F 500) using an abrasion and washingresistance tester (Erichsen, 5 brush with hog's bristles). The glossbefore and 10 min after the abrading is determined with a reflectometer(20 ° irradiation angle).

TABLE 5 Summary of the properties of the liquid lacquers relevant interms of lacquer technology, and of the applied and dried films. Priorart Silica 1 Silica 4 Reference Grindometer value [μm] <10 <10 <10 /Viscosity (millbase) [mPas]  6 rpm 58 30 26 30 60 rpm 48 43 33 40 Wavescan long wave 4.8 1.2 1.1 1.4 short wave 6.5 3.0 3.1 4.7 20°reflectometer value 89.0 90.2 89.6 90.8 before scratching Haze beforescratching 4 4 3 4 40 strokes with Sikron F 500 78.3 85.9 86.2 55.3Residual gloss [%]

It is shown that a substantially better improvement in the residualgloss is achieved after a scratch stressing of the lacquer surface byusing the silicas according to the invention than with the prior art. Inaddition, owing to their low rheological efficiency, the silicasaccording to the invention do not cause an orange-peel effect.

1. Silanised, structurally modified, pyrogenically produced silicas,characterised by groups fixed to the surface, wherein the groups aredimethylsilyl and/or monomethylsilyl, said silicas having a tampeddensity of 280 g/l or less, said silicas having been structurallymodified by being ball milled and being characterised by the followingphysico-chemical characteristics: BET surface area m²/g: 25-400 Averagesize of the primary particles nm: 5-50 pH value: 3-10 Carbon content %:0.1-10   DBP value %: <200.


2. Process for the production of the silanised, structurally modified,pyrogenically produced silica according to claim 1, characterised inthat pyrogenically produced silica is treated by a known method withdimethyldichlorosilane and/or monomethyltrichlorosilane, the groupsdimethylsilyl and/or monomethylsilyl being fixed on the surface of thepyrogenic silica, and is then structurally modified by ball milling thesilica and optionally post-ground.
 3. Process for the production of thesilanised, structurally modified, pyrogenically produced silicaaccording to claim 2, characterised in that a tempering takes placeafter the structural modification and/or post-grinding.
 4. A method forimproving the scratch resistance of lacquers comprising incorporatinginto the lacquer the silanized, structurally modified, pyrogenicallyproduced silicas defined in claim
 1. 5. A silanised, structurallymodified, pyrogenically produced and ball milled silica having groupsfixed to the surface wherein said groups comprise at least one ofdimethylsilyl and monomethylsilyl and wherein said silica has a tampeddensity of 280 g/l or less, said silica having the following physicalchemical properties: BET surface area m²/g: 25-400 Average size of theprimary particles nm: 5-50 pH value: 3-10 Carbon content %: 0.1-10   DBPvalue %: <200.


6. The silanised, structurally modified, pyrogenically produced silicaaccording to claim 5, which has a tamped density of 100 to 280 g/l.
 7. Aprocess for the production of a silanised, structurally modified,pyrogenically produced silica of claim 5, comprising: treating apyrogenically produced silica with at least one ofdimethyldichlorosilane and monomethyltrichlorosilane to thereby fixgroups on the surface of the pyrogenic silica, said groups being atleast one of dimethylsilyl and monomethylsilyl, structurally modifyingsaid silica by ball milling said silica and optionally post grindingsaid silica.
 8. The process according to claim 7, further comprisingtempering after at least one of structurally modifying said silica andpost grinding said silica.
 9. The process according to claim 8, whereinpost grinding is by air-jet mill or pin mill.
 10. The process accordingto claim 8, wherein tempering takes place under protective gas.
 11. Alacquer comprising a polyurethane and a silanised silica having beenstructurally modified by being ball milled and being characterised bythe following physico-chemical characteristics: BET surface area m²/g:25-400 Average size of the primary particles nm: 5-50 pH value: 3-10Carbon content %: 0.1-10   DBP value %: <200.

said silica having a tamped density of 285 g/l or less.
 12. A surfacecoated with the lacquer according to claim
 11. 13. The surface accordingto claim 12, which is metal.